This protein is involved in the repair of methylated DNA. Unlike EC 3.2.2.20, DNA-3-methyladenine glycosidase I and EC 3.2.2.21, DNA-3-methyladenine glycosidase II, which remove the methylated base leaving an apurinic/apyrimidinic site, this enzyme transfers the methyl group from the methylated DNA to an internal cysteine residue, leaving an intact nucleotide. Since the methyl transfer is irreversible, the enzyme can only catalyse a single turnover.

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the enzyme functions in DNA repair by direct dealkylation of mutagenic 6-O-alkylguanine. The protein methylated at Cys69 becomes a transcriptional activator of the genes in the ada regulon, including its own

6-O-methylguanine is an important adduct formed by methylating agents, that, if not repaired, can lead to mutations and death. Its repair is carried out by 6-O-methylguanine DNA-methyltransferase. Exposure of E. coli cells to sublethal concentrations of methylating agent triggers the expression of the gene

the binding to DNA is the rate determining step in the repair process. Approximately eight base pairs of the DNA substrate are covered by the human enzyme. Binding affinity to methylated DNA is two times higher than that to unmodified DNA. The interaction with DNA induces a conformational change in the enzyme

DNA hypermethylation and silencing of MGMT are frequent and rather early events in esophageal squamous cell carcinogenesis. Hypermethylation and inactivation of MGMT may be prevented or reversed by dietary polyphenols, (-)-epigallocatechin-3-gallate and genistein, for the prevention of carcinogenesis

key enzyme in DNA repair network. Hypermethylation of the CpG island located in the promoter region of MGMT is primarily responsible for the loss of enzyme function in many tumor types. The methylation mediated silencing of MGMT has two consequences for cancer. First, tumors with MGMT methylation have a new mutator phenotype characterized by the generation of transition point mutations in genes involved in cancer etiology, such as the tumor suppressor p53 and the oncogene K-ras. Second, MGMT hypermethylation demonstrates the possibility of pharmacoepigenomics: methylated tumors are more sensitive to the killing effects of alkylating drugs used in chemotherapy

the 28-amino acid carboxy-terminal tail of the enzyme is not required for activity and modulates the rate of 6-O-methylguanine DNA methyltransferase repair at reduced temperatures and plays a role in substrate specificity

binding of AGT to single-stranded DNAs ranging in length from 5 to 78 nucleotides, binding is moderately cooperative, resulting in an all-or-nothing association pattern on short templates binding density

in the catalytic demethylation of DNA containing 6-O-methylguanine, roles of six amino acids, i.e., Cys145, His146, Glu172, Tyr114, Lys165, and Ser159 are involved. At the first step, Cys145 in the Cys145-water-His146-Glu172 tetrad is converted to cysteine thiolate anion while at the second step, abstraction of the Tyr114 proton by the N3 site of DNA containing 6-O-methylguanine occurs in a barrierless manner. In the third step, abstraction of Lys165 proton by deprotonated Tyr114 and transfer of the methyl group of DNA containing 6-O-methylguanine to the thiolate group of Cys145 anion occur simultaneously.

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the DNA repair protein O6-alkylguanine-DNA alkyltransferase is a principal mechanism of cellular resistance to the toxic and mutagenic effects of DNA damage produced by certain monofunctional alkylating agents. ATase operates by the transfer of the offending alkyl groups from the O6 position of guanine and the O4 position of thymine in damaged DNA to a cysteine residue at the active site of the protein. This is an irreversible process that results in the stoichiometric inactivation of the protein

the enzyme functions in DNA repair by direct dealkylation of mutagenic 6-O-alkylguanine. The protein methylated at Cys69 becomes a transcriptional activator of the genes in the ada regulon, including its own

6-O-methylguanine is an important adduct formed by methylating agents, that, if not repaired, can lead to mutations and death. Its repair is carried out by 6-O-methylguanine DNA-methyltransferase. Exposure of E. coli cells to sublethal concentrations of methylating agent triggers the expression of the gene

DNA hypermethylation and silencing of MGMT are frequent and rather early events in esophageal squamous cell carcinogenesis. Hypermethylation and inactivation of MGMT may be prevented or reversed by dietary polyphenols, (-)-epigallocatechin-3-gallate and genistein, for the prevention of carcinogenesis

key enzyme in DNA repair network. Hypermethylation of the CpG island located in the promoter region of MGMT is primarily responsible for the loss of enzyme function in many tumor types. The methylation mediated silencing of MGMT has two consequences for cancer. First, tumors with MGMT methylation have a new mutator phenotype characterized by the generation of transition point mutations in genes involved in cancer etiology, such as the tumor suppressor p53 and the oncogene K-ras. Second, MGMT hypermethylation demonstrates the possibility of pharmacoepigenomics: methylated tumors are more sensitive to the killing effects of alkylating drugs used in chemotherapy

in bacterial expression systems, recombinant hAGT is produced in increasingly larger quantities when growth media are supplemented with up to 0.1 mM ZnCl2. Metal-enriched hAGT samples have a 5fold increase in repair rate constant over conventionally purified protein samples and a 60fold increase over metal-stripped hAGT. Zinc confers a mechanistic enhancement to repair activity that does not result from an increase in substrate binding affinity. Zinc also provides conformational stability to hAGT that may influence its regulation

inactivates purified AGT and mutant R128A to approximately the same extent; inactivates purified AGT and mutant R128A to approximately the same extent, small reduction in the loss of activity in the absence of DNA, but no effect at all in the presence of DNA, inactivates mutant Y114A much less than wild-type, and DNA completely prevents this inactivation, mutants P140K and Y158H are less inactivated than wild-type AGT, specifically in the presence of DNA

can directly alkylate the active site of the enzyme, the agent can increase the effectiveness of environmental and endogenously produced alkylating carcinogens in producing the mutagenic 6-O-alkylguanine residue in DNA in vivo

methyl isocyanate resulting from base-catalyzed activation of VNP40101M inhibits the enzyme, thereby enhancing the yield of the DNA G-C interstrand crosslink responsible for the antitumor activity of this agent

30times more active than O6-benzylguanine against the wild-type alkyltransferase, inactivation of P140K mutant alkyltransferase. Inhibitor shows promise as an agent for possible tumor-selective alkyltransferase inactivation superior toO6-benzylguanine as a chemotherapy adjuvant

methyl isocyanate resulting from base-catalyzed activation of VNP40101M inhibits the enzyme, thereby enhancing the yield of the DNA G-C interstrand crosslink responsible for the antitumor activity of this agent

TMZ; tumor cells with high levels of MGMT and/or with a defective DNA mismatch repair are resistant to temozolomide, hyperthermia significantly enhances temozolomide cytotoxicity in mismatch repair-proficient cells, either endowed or not with MGMT activity, and in mismatch repair-deficient cells, hyperthermia alone does not affect MGMT activity, but enhances the enzyme depletion induced by temozolomide treatment

transferase activity methylates itself on removal of the methyl group from the 6-O position of guanine. Modification of a reactive sulfhydryl group can account for the enzyme inactivation accompanying the reaction

high level of enzyme in tumors and relative resistance to cyclophosphamide in lung cancer indicates that 6-O-methylguanine-DNA methyltransferase may be a predictive factor of resistance to cyclophosphamide

structure analysis by multinuclear multidimensional NMR spectroscopy, a two-domain protein with an alpha/beta fold, N-terminal domain consists of a three-stranded antiparallel beta sheet, N-terminus is somewhat less well defined than the C-terminus, structure is similar to homologs from other organisms that have been determined by crystallography, with some variation in the N-terminal domain, whereas the C-terminal domain is more highly conserved in both sequence and structure

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Crystallization/COMMENTARY

ORGANISM

UNIPROT

LITERATURE

Cys acceptor site is buried in the protein and, in order for reaction with a DNA substrate to take place, a change in conformation of either the substrate or the protein must occur, Glu-172 and Asn-137 play a major structural role in the AGT protein

ligated into the pHybLex/Zeo plasmid and electroporated into Escherichia coli XL1-Blue, yielding a library of at least 320000 independent clones, genes of selected AGT mutants subcloned into the pGEX-2T plasmid, allowing for the expression of the AGT mutants as GST fusion proteins

there is a good correlation between the increasing MGMT promoter methylation and decreased MGMT expression, in most patients who has been treated with temozolomide, there is decreased MGMT expression in the post treatment sample when compared to the primary sample

called MAGT with 15 different mutations in a single protein, has23fold increase in activity relative to wild-type, is resistant against N9-substituted BG derivatives used for inhibition of wild-type, shows suppressed affinity towards DNA

substantially reduced AGT-mediated increase in toxicity and the induction of mutations in Escherichia coli cells treated with Br(CH2)2Br, is able to react with Br(CH2)2Br at the Cys145 acceptor site, but the resulting AGT-Cys145S-(CH2)2Br is much less able to produce a covalent adduct with DNA

binds to alkylated DNA in a similar manner to wild type AGT but is unable to carry out the repair transfer, expressed in Escherichia coli, this mutant increases killing and mutagenesis by N-methyl-N'-nitro-N-nitrosoguanidine

no major structural change upon energy minimization, is in the vicinity of the active Cys145 and may cause disturbances of O6-alkyl transfer from DNA to the protein, does not affect DNA repair capacity

the L84F polymorphic variant of human O6-methylguanine-DNA methyltransferase alters stability in U87MG glioma cells but not temozolomide sensitivity, upon exposure to O6-benzylguanine, the L84F variant is degraded more rapidly than wild type

deletion of more than 8 or 31 residues from the amino or carboxyl terminus, respectively, leads to the loss of both activity and substrate binding. Removal of Arg9 or Leu176 and distal residues inactivates the protein

three allelic variants: V1 with amino acid substitution Leu84Phe, variant V2 with amino acid substitution Trp65Cys and variant V3 with a silent mutation. Wild-type and V1 variant have similar enzymatic and physicochemical properties, while variant V2 is considered to be unstable and rare

the 28-amino acid carboxy-terminal tail of the enzyme is not required for activity and modulates the rate of 6-O-methylguanine DNA methyltransferase repair at reduced temperatures and plays a role in substrate specificity

insertion of random amino acid loops into the protein backbone reveals mutants that react with the non-natural substrate O6-propargylguanine, libraries generated by conventional random or targeted saturation mutagenesis, by contrast, do not yield any mutants with activity towards this new substrate

mutation of Arg-128 to Ala greatly reduces the ability of AGT to repair O6-methylguanine in DNA but has no effect on the alkyl transfer reaction when the free base substrate, O6-benzylguanine is used, stability of AGT is reduced by most mutations at Lys-165

MAGT decreased activity can be restored by combination of saturation mutagenesis of residues 150-154 and 31-35 from phage display and yeast three-hybrid system selections, reveals a mutant with 17fold higher activity than MAGT and a 52fold higher activity than wild-type AGT, is the most active AGT mutant against O6-benzylguanine derivatives described so far

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Renatured/COMMENTARY

ORGANISM

UNIPROT

LITERATURE

renaturation by dilution with buffer from 8 M urea or 6 M guanidine HCl instantly restores the secondary structure of the Ada protein to a state that is almost indistinguishable from the native state. Kinetics of renaturation is fast, at 0°C the restoration is quantitative in less than 30 s. The heat-coagulated protein can be restored to full activity by cycling it through treatment with 8 M urea or 6 M guanidine

introduction of the MS-MLPA assay may not only be helpful for predicting response of gliomas to temozolomide, but may also facilitate tailor-made treatment with other chemotherapeutic agents for a variety of tumors

highly effective inactivation of MGMT by an oligodeoxyribonucleotide containing O6-(4-bromothenyl)guanine suggests that such oligodeoxyribonucleotides might have therapeutic applications if problems of delivery can be addressed

strategy of loop insertion to alter enzyme specificity shall be general and applicable to other classes of proteins, the isolated AGT mutant can be applied in molecular imaging, where the mutant and parental AGTs are used to label two different AGT fusion proteins with different fluorophores in the same living cell or in vitro, allows establishment of fluorescence-based assays to detect protein-protein interactions and measure enzymatic activities

N-terminal domain plays a critical structural role in maintaining an active configuration of the C-terminal domain, N-hAGT and C-hAGT domains can protect from N-methyl-N'-nitro-N-nitrosoguanidine in Escherichia coli GWR-109 cells

ability to specifically label AGT fusion proteins in the presence of endogenous AGT, after brief incubation of the cells with a small-molecule inhibitor, may significantly broaden the scope of application of AGT fusion proteins for studying protein function in living cells

high level of enzyme in tumors and relative resistance to cyclophosphamide in lung cancer indicates that 6-O-methylguanine-DNA methyltransferase may be a predictive factor of resistance to cyclophosphamide

the enzyme is important in cellular resistance to certain alkylating antitumor agents such as the methylating drug temozolomide. Cisplatin is able to decrease enzyme levels in Jurkat cells, probably via the inhibition of gene transcription. The clinical efficiacy of triazene compounds might be improved by combination with cisplatin using appropriate doses and schedules of administration

the efficiacy of 6-O-benzylguanine as a chemomodulator depends on the extent of depletion of 6-O-methylguanine DNA methyltransferase in normal tissues and the optimal therapeutic index for combination of 6-O-benzylguanine and 1,3-bis(2-chloroethyl)-1-nitrosourea therapy should be achieved by depleting 6-O-methylguanine DNA methyltransferase in the target tumor for 24 h with minimal depletion in normal tissues

DNA hypermethylation and silencing of MGMT are frequent and rather early events in esophageal squamous cell carcinogenesis. Hypermethylation and inactivation of MGMT may be prevented or reversed by dietary polyphenols, (-)-epigallocatechin-3-gallate and genistein, for the prevention of carcinogenesis

O4-benzylfolic acid is 30times more active than O6-benzylguanine against the wild-type alkyltransferase, inactivation of P140K mutant alkyltransferase. Inhibitor shows promise as an agent for possible tumor-selective alkyltransferase inactivation superior toO6-benzylguanine as a chemotherapy adjuvant

combining cisplatin and temozolomide is based on the potential for improved antitumour activity, combination is well tolerated in children and adolescents, generating no toxicity greater than that of the single agents

even slight alterations in the active site pocket of AGT do not prevent its ability to protect cells from alkylating agents, can block the paradoxical enhancement of the genotoxicity of the larger alpha,omega-dihaloalkanes by reducing the reaction with Cys145

cigarette smoking not only induces O6-alkylguanine lesions, it inhibits the repair of these adducts by MGMT, O6-alkylguanine adducts are well established carcinogenic lesions and decreased repair of such lesions may increase susceptibility to lung cancer in smokers

inhibition of tumour MGMT by pseudosubstrates to overcome tumour resistance is under clinical evaluation, MGMT overexpression in haematopoietic stems cells has been shown to protect normal cells against the myelosuppressive effects of chemotherapy

the results suggest that expression of MGMT could enhance the capacity of bone marrow-derived cells to repopulate lung epithelium, and when used in combination with a gene of interest, MGMT could have therapeutic applications

determination of MGMT in peripheral blood mononuclear cells can identify patients at greatest risk of toxicity with O6-alkylating agent chemotherapy or who are suitable for dose intensification, MGMT protects against the toxic effects of O6-alkylating agents

Comparison of single- versus double-bolus treatments of O6-benzylguanine for depletion of O6-methylguanine DNA methyltransferase (MGMT) activity in vivo: development of a novel fluorometric oligonucleotide assay for measurement of MGMT activity

Careful exclusion of non-neoplastic brain components is required for an appropriate evaluation of O6-methylguanine-DNA methyltransferase status in glioma: relationship between immunohistochemistry and methylation analysis

The prognostic impact of O6-methylguanine DNA methyltransferase and epidermal growth factor receptor expressions on primary gliosarcoma: a clinicopathologic and immunohistochemical study of seven cases at a single institution